Proprotein convertase subtilisin kexin 9 (PCSK9) is a member of the subtilisin serine protease family. The other eight mammalian subtilisin proteases, PCSK1-PCSK8 (also called PC1/3, PC2, furin, PC4, PC5/6, PACE4, PC7, and S1P/SKI-1) are proprotein convertases that process a wide variety of proteins in the secretory pathway and play roles in diverse biological processes (Bergeron. F. (2000) J. Mol. Endocrinol. 24, 1-22, Gensberg, K., (1998) Semin. Cell Dev. Biol. 9, 11-17, Seidah, N. G. (1999) Brain Res. 848, 45-62, Taylor, N. A., (2003) FASEB J. 17, 1215-1227, and Zhou, A., (1999) J. Biol. Chem. 274, 20745-20748). PCSK9 has been proposed to play a role in cholesterol metabolism. PCSK9 mRNA expression is down-regulated by dietary cholesterol feeding in mice (Maxwell, K. N., (2003) J. Lipid Res. 44, 2109-2119), up-regulated by statins in HepG2 cells (Dubuc, G., (2004) Arterioscler. Thromb. Vasc. Biol. 24, 1454-1459), and up-regulated in sterol regulatory element binding protein (SREBP) transgenic mice (Horton, J. D., (2003) Proc. Natl. Acad. Sci. USA 100, 12027-12032), similar to the cholesterol biosynthetic enzymes and the low-density lipoprotein receptor (LDLR). Furthermore. PCSK9 missense mutations have been found to be associated with a form of autosomal dominant hypercholesterolemia (Hchola3) (Abifadel, M., et al. (2003) Nat. Genet. 34, 154-156, Timms, K. M., (2004) Hum. Genet. 114, 349-353, Leren, T. P. (2004) Clin. Genet. 65, 419-422). PCSK9 may also play a role in determining LDL cholesterol levels in the general population, because single-nucleotide polymorphisms (SNPs) have been associated with cholesterol levels in a Japanese population (Shioji, K., (2004) J. Hum. Genet. 49, 109-114).
Autosomal dominant hypercholesterolemias (ADHs) are monogenic diseases in which patients exhibit elevated total and LDL cholesterol levels, tendon xanthomas, and premature atherosclerosis (Rader, D. J., (2003) J. Clin. Invest. 111, 1795-1803). The pathogenesis of ADHs and a recessive form, autosomal recessive hypercholesterolemia (ARH) (Cohen, J. C., (2003) Curr. Opin. Lipidol. 14, 121-127), is due to defects in LDL uptake by the liver. ADH may be caused by LDLR mutations, which prevent LDL uptake, or by mutations in the protein on LDL, apolipoprotein B, which binds to the LDLR. ARH is caused by mutations in the ARH protein that are necessary for endocytosis of the LDLR-LDL complex via its interaction with clathrin. Therefore, if PCSK9 mutations are causative in Hchola3 families, it seems likely that PCSK9 plays a role in receptor-mediated LDL uptake.
Overexpression studies point to a role for PCSK9 in controlling LDLR levels and, hence, LDL uptake by the liver (Maxwell, K. N. (2004) Proc. Natl. Acad. Sci. USA 101, 7100-7105, Benjannet, S., et al. (2004) J. Biol. Chem. 279, 48865-48875, Park, S. W., (2004) J. Biol. Chem. 279, 50630-50638). Adenoviral-mediated overexpression of mouse or human PCSK9 for 3 or 4 days in mice results in elevated total and LDL cholesterol levels; this effect is not seen in LDLR knockout animals (Maxwell, K. N. (2004) Proc. Natl. Acad. Sci. USA 101, 7100-7105, Benjannet, S., et al. (2004) J. Biol. Chem. 279, 48865-48875, Park, S. W., (2004) J. Biol. Chem. 279, 50630-50638). In addition. PCSK9 overexpression results in a severe reduction in hepatic LDLR protein, without affecting LDLR mRNA levels, SREBP protein levels, or SREBP protein nuclear to cytoplasmic ratio.
Loss of function mutations in PCSK9 have been designed in mouse models (Rashid et al., (2005) PNAS, 102, 5374-5379), and identified in human individuals (Cohen et al. (2005) Nature Genetics 37:161-165). In both cases loss of PCSK9 function lead to lowering of total and LDLc cholesterol. In a retrospective outcome study over 15 years, loss of one copy of PCSK9 was shown to shift LDLc levels lower and to lead to an increased risk-benefit protection from developing cardiovascular heart disease (Cohen et al., (2006) N. Engl. J. Med., 354:1264-1272).
X-box binding protein 1 (XBP-1) is a basic leucine zipper transcription factor that is involved in the cellular unfolded protein response (UPR). XBP-1 is known to be active in the endoplasmic reticulum (ER). The ER consists of a system of folded membranes and tubules in the cytoplasm of cells. Proteins and lipids are manufactured and processed in the ER. When unusual demands are placed on the ER, “ER stress” occurs. ER stress can be triggered by a viral infection, gene mutations, exposure to toxins, aggregation of improperly folded proteins or a shortage of intracellular nutrients. The result can be Type II diabetes, metabolic syndrome, a neurological disorder or cancer.
Two XBP-1 isoforms are known to exist in cells: spliced XBP-1S and unspliced XBP-1U. Both isoforms of XBP-1 bind to the 21-bp Tax-responsive element of the human T-lymphotropic virus type 1 (HTLV-1) long terminal repeat (LTR) in vitro and transactivate HTLV-1 transcription. HTLV-1 is associated with a rare form of blood dyscrasia known as Adult T-cell Leukemia/lymphoma (ATLL) and a myelopathy, tropical spastic paresis.
Double-stranded RNA molecules (dsRNA) have been shown to block gene expression in a highly conserved regulatory mechanism known as RNA interference (RNAi). WO 99/32619 (Fire et al.) disclosed the use of a dsRNA of at least 25 nucleotides in length to inhibit the expression of genes in C. elegans. dsRNA has also been shown to degrade target RNA in other organisms, including plants (see, e.g., WO 99/53050, Waterhouse et al.; and WO 99/61631, Heifetz et al.), Drosophila (see, e.g., Yang, D., et al., Curr. Biol. (2000) 10:1191-1200), and mammals (see WO 00/44895, Limmer; and DE 101 00 586.5, Kreutzer et al.). This natural mechanism has now become the focus for the development of a new class of pharmaceutical agents for treating disorders that are caused by the aberrant or unwanted regulation of a gene.
A description of siRNA targeting PCSK9 can be found in U.S. patent application Ser. No. 11/746,864 filed on May 10, 2007 (now U.S. Pat. No. 7,605,251) and International Patent Application No. PCT/US2007/068655 filed May 10, 2007 (published as WO 2007/134161). Additional disclosure can be found in U.S. patent application Ser. No. 12/478,452 filed Jun. 4, 2009 (published as US 2010/0010066) and International Patent Application No. PCT/US2009/032743 filed Jan. 30, 2009 (published as WO 2009/134487).
A description of siRNA targeting XPB-1 can be found in U.S. patent application Ser. No. 12/425,811 filed on Apr. 17, 2009 and published as US 2009-0275638.
Dual targeting siRNAs can be found in International patent application publication no. WO/2007/091269.